1. Field of the Invention
The present invention relates to an apparatus for detecting linear motion of objects, specifically to a photocell device functioning in either a photoconductive, photovoltaic or photoresistive mode with electrical outputs that can be used to generate useful information such as velocity, position, and paths of projectiles or other objects.
2. Prior Art
The location and motion characteristics of projectiles are of great interest, whether taking the form of bullets, artillery rounds, baseballs, golf balls or other objects. When a projectile of interest is small and moving relatively fast, the detection, location and quantification of the motion of the projectile with high degrees of accuracy and reliability are challenging. Numerous devices have been devised to perform one or more such functions, particularly with respect to weapons firing ranges.
Some devices utilizing transducers or similar shock or acoustic wave detectors require the projectile of interest to impact a target so that the impact point can be determined. The signals from such detectors are fed into a calculating device that calculates the position of the bullet or other projectile, causing the position to be displayed or stored. Systems of this general type are disclosed in U.S. Pat. No. 2,973,964 (Zito), U.S. Pat. No. 3,678,495 (Gilbert), U.S. Pat. No. 5,095,433 (Botarelli et al.), and U.S. Pat. No. 4,514,621 (Knight).
Other devices use direct or indirect lighting in beam arrangements that permit triangulation based on reflections or direct impingement of light relative to reference lines as in U.S. Pat. No. 3,807,858 (Finch). Some apparatus merely detect the passing of an object through an area, as in the case of U.S. Pat. No. 4,870,267 (Beeckel) and U.S. Pat. No. 3,788,748 (Knight et al.).
More complex apparatus employ active means such as radar or scanning laser devices to determine time-of-arrival and angle-of-arrival information using reflected radio or light energy responses to detect and track projectiles. Radar is very expensive, can produce potentially harmful emanations, and is quite bulky. Whether simple or complex, the projectile sensing devices heretofore known suffer from a variety of disadvantages:
(a) The prior art apparatus generally only provide position or velocity, not both. None provide adequate information for calculation of a projectile""s flight path so that its point of origin or destination, or its location in space can be calculated for any given time along the object""s path. Different specific devices are required to capture different parameters. While some may provide a position of a projectile by virtue of its impact on a target or surface, locating the object in free space requires a different apparatus, which does not provide velocity information. Other devices may provide velocity, but not position or location.
(b) Most prior art is limited in the dynamic range of certain parameters, such as velocities within relatively narrow ranges. For example, a device may only be capable of capturing velocities of supersonic or hypersonic projectiles, but not subsonic.
(c) Many prior solutions require prior knowledge of an object""s precise path of travel.
(d) The utility and accuracy of some of the prior art systems diminish as the target material degrades, and sometimes a detector component is damaged or degraded by projectile perforations.
(e) Their functionality requires complex pre-arrangement of system components. In some cases, reflective panels are required to be positioned opposite multiple sensors, whereby ambient conditions are controlled, or reference lines are in view of the sensing device. More complex systems, such as those employing radar, require complex calibration methods to ensure accuracy.
(f) Some prior art projectile detectors require the use of delicate and damage-prone microphones or transducers that require frequent repair or replacement.
In accordance with the present invention a projectile sensor comprises a specially shaped or exposed photocell and a lens means mounted within a support means. The passing of a projectile within the field of view of the sensor causes several momentary changes in the amount of photonic energy impinging on the sensitive areas of the photocell which in turn causes measurable electrical responses from the photocell. The times of the electrical responses and the ratios of the time periods between the electrical responses relate to the velocity and position of the projectile.
Accordingly, the objects and advantages of the present invention are:
(a) to provide a projectile sensor that combines many capabilities and characteristics into a single device or several identical devices with intersecting fields of view, including the ability to allow both velocity and position in space to be determined accurately;
(b) to provide a projectile sensor that permits the derivation of accurate position data across wide ranges of projectile sizes and velocities and at high repetition rates;
(c) to provide a projectile sensor that can support measurements of projectiles randomly originating from a range of angles in both the horizontal and vertical planes, while providing the means to predict the origin, destination, and path of any of the projectiles;
(d) to provide a projectile sensor that can support the accurate determination of a projectile""s position, angle-of-arrival, and velocity as it passes through an imaginary plane in lieu of a physical target or surface, thereby avoiding degradation due to projectile impacts or perforations;
(e) to provide a projectile sensor with relatively simple and flexible emplacement options, alignment, and calibration, capable of operating across a wide range of ambient conditions;
(f) to provide a projectile sensor that is durable and reliable;